How would i curve panels like this?
You may do it using a Spin Tool. In right view add a single vertex and extrude it creating the arch's profile. In Object Mode press Shift+C to place the cursor in the center of a grid. In Edit Mode grab the profile and translate it along the Z axis. Press the Spin button in a tool shelf. Your arch is ready.


You can model a niche in the same way. After spinning it divide it using loopcuts (Ctrl+R). Then extrude single segments downwards as pictured below. You have a clean geometry to add creasing loopcuts for the Subsurf Modifier.


Finally join the meshes with Ctrl+J, remove doubles and give the object a Mirror Modifier.